Telescoping sleeve heater

ABSTRACT

A fluid heater, primarily for water, wherein the hot combustion gases and heat-absorbing fluid flow through separate sinuous passage systems formed by four telescoping sleeves and radially spaced partitions in the annular spaces between adjacent sleeves.

United States Patent Raymond A; Hemmert lnventor Williamsville. N.Y.Appl. No. 849,036 Filed Aug. 11. 1969 Patented Aug. 3, 1971 AssigneeAmerican Radiator 81 Standard Sanitary Corporation New York, N.Y.

TELESCOPING SLEEVE HEATER 11 Claims, 14 Drawing ri 1.1. CI r221 7/12Field 01 Search 122/136, 149, 37

[56] References Cited UNITED STATES PATENTS 2,040,959 5/1936 Schumann122/136 2,287,057 6/1942 Page 122/149 3,120,838 2/1964 Mueller 122/149FOREIGN PATENTS 787,261 7/1935 France 122/149 930,417 7/1963 GreatBritain 122/136 Primary Examinerl(enneth W. Sprague Attorneys-John E.McRae, Tennes 1. Erstad and Robert G.

Crooks ABSTRACT: A fluid heater, primarily for water, wherein the hotcombustion gases and heat-absorbing fluid flow through separate sinuouspassage systems formed by four telescoping sleeves and radially spacedpartitions in the annular spaces between adjacent sleeves.

PATENTED AUB 3 l97| SHEET 1 BF 3 INVENTOR.

PATENTED AUG 3 Bil SHEEY 2 BF 3 INVENTUR. PAv/volva 4. Han/veer PATENTEDAll; 3 Eh sum 3 or 3 FIG. 1B

IN VEN TOR. PA VMONO A). HEMMEAT TELESCOPING SLEEVEHEATER THE DRAWINGSFIGS. 1 and 5 are sectional views of a heater built under the 1 5invention; the FIGS. are taken on line 1-1 in FIGS. 2.

FIG. 2 is a sectional view taken on line 2-2 in FIG. 1.

FIGS. 3, 4, 8, 9, and 11 are fragmentary sectional views showing detailsof construction that may be used in lieu of certain details shown inFIG. 1.

FIG. 6 is a fragmentary sectional view on a reduced scale, taken on line6-6 in FIG. 1.

FIG. 7 is a fragmentary plan view looking down on the heater of FIG. 1.

FIG. 12 is a sectional view of another embodiment of the invention takenon line 12-12 in FIG. 13.

FIG. 13 is asectional view on line 13-13 in FIG. 12.

FIG. 14 is a perspective view schematically illustrating a feature ofconstruction used in the FIG. 12 embodiment.

FIG. 1

The heater of FIG. 1 comprises four concentric sleeves 10, 12, 14 and 16suitably connected to a front closure plate 18. Sleeves 10 and 12 havetheir front end edges seam welded to plate 18, as at 20 and 22. Sleeves14 and 16 have their front edges seam welded to an annular seal plate24. Bolts 26 may run through holes in the peripheral face areas of thetwo plates 18 and 24, to removably connect said plates together. FIG. 5shows the inner assembly (members 10, 12 and 18) partially removed fromthe outer assembly (members 14, 16 and 24), as during the process offabrication or during maintenance periods.

The rear. end edge of sleeve 16 is seam welded to an ellipticallycontoured rear closure plate 28, and the rear end edge of sleeve 14 iswelded to an elliptically contoured rear closure plate 30. Plates 28 and30 can be flat; however the assembly is stronger when the plates areelliptical. The rear end edges of sleeves 10 and 12 are welded to a flatrear closure plate 32, said plate having a circular opening 34therethrough for communicating the central sleeve space 36 with the gasreversal zone 38 located forwardly of plate 30. v

The annular space between sleeves l0 and 12 forms a primaryheat-absorbing fluid chamber; it is subdivided into two longitudinalpassages by two radial partitions 62 and 64. The annular space betweensleeves l2 and 14 forms a secondary hot gas chamber; it is subdividedinto three passages by three radial partitions 72, 44 and 52. Theannular space between sleeves 14 and 16 forms a secondary heat-absorbingfluid chamber; it is subdivided into longitudinal passages by two radialpartitions 78 and 80.

HOT GAS PASSAGE SYSTEM Heat may be supplied to the heater by means of aconventional gas or oil burner 40 arranged to discharge the fuel-gasinto sleeve 10. Sleeve 10 constitutes a combustion tube for reception ofthe burning gas flowing toward the opening 34. As the hot gases impingeagainst wall 30 they are deflected or directed through a sectorlikeopening 41 in plate 32, and thence into a longitudinal passage 45 formedbetween sleeves 12 and 14. As shown in FIG. 2, passage 45 is furtherdefined by two longitudinal radial partitions 42 and 44 spaced from oneanother by about.l50 radial degrees. Opening 41 has the same shape andflow area as passage 45 so that one is the continuation of the other.The hot gases proceed forwardly through passage 45 until they reach thefront edge 46 of partition 42, whereupon they pass through therectangular opening 48 formed between the partition edge 46 and thefront closure plate 18.

After passing through the opening 48 the gases are caused to moverearwardly in a second longitudinal passage 50 defined by the twocylinders 12 and 14, and the two radial partitions 42 and 52. Passage 52is about 120 radial degrees as measured in F IG 2. The rearwardlyflowing hot gases strike 7 against the front face of a baffle 32a eformed as part plate 32. As shown in FIG. 6, baffle 32a extends about 2l0 radial degrees with respect to the tube axis so asto blank off thethe arcuate space going from partition 42,through 52 and to 44. Baffle32a is exposed to very hot gases on both its front surface and its backsurface; it must therefore be formed of heat resistant material. Perhapsa better expedient is to form the baffle as a water-cooled baffle as awater-cooled baffle, as shown in FIG. 4, to be described hereafter.

As the gas in passage 50 strikes the front face of baffle 320 it isdeflected upwardly through an opening formed between the the rear edgeof partition 52 and the baffle32a. The described opening is similar inshape and'size to the previously described opening 48, but is located atthe rear extremity of partition 52. The gases move through this openinginto a longitudinal passage 54 formed by the partitions 52 and 44. Asshown by the arrows in FIG. 1, the hotgases flow forwardly and outthrough a stack 56 suitably welded to sleeve 14 and projecting throughthe sleeve 16 as a sealed connection.

It will be noted that segmental gas passage 45 covers 150 radialdegrees, whereas gas passage 50 covers I20 radial degrees, and gaspassage 54 covers only 90 radial degrees. Passage 45 thus has thegreatest cross section, and passage 54 has the smallest. As the gasproceeds through the passage system it becomes cooler and its densitydecreases. By progressively reducing the passage cross section thelinear gas velocity can be kept fairly constant throughout its travelthrough the heater, thereby achieving best scrubber action of all theheat transfer surface.

FLUID PASSAGE SYSTEM The fluid to be heated may be water, oil or otherliquid; alternately the fluid can be a gas'such as air. The design ofthe heater makes it particularly useful in heating liquids which havegreater heat-absorbing abilities then gases. v

The fluid is introduced to the heater through a tubular fluid inlet 58mounted on the front closure plate 18in direct registry with a passage60 formed by the sleeves 10 and 12. As best shown in FIG. 2, passage 60is further defined by two radial partitions 62 and 64 suitably welded tosleeve 10. Fluid flows through passage 60 in a rearward direction untilit reaches the rear edges 66 of partitions 62 and 64. The open spacebetween the partition edges 66 and the closure plate 32 allows thefluidto flow upwardly into a second passage 68, as denoted by arrows 70. g I

Fluid flows forwardly in passage 68 and exits through a crossover' pipe72 which is mounted on the front closure plate 18. Pipe 72 is directedlaterally; rearwardly, and then back to sleeve 16 to conduct the fluidinto the segmental passage 74 formed between the sleeves l4 and 16. Thefull extent of pipe 72 is not visible in FIG. 1, but its operationalconnection is denoted in FIG. 1 by the directional line 76.

Preferably the crossover pipe 72 is mounted on the external surfaces ofthe heater so that the pipe can be disconnected or removed withoutdisturbing the various concentric cylinders. By so locating the pipe theinner assembly (closure plate 18 and sleeves 10 and'12) can'be removedfrom the space circumscribed by sleeve 14 without interference from pipe72. FIG. 7 shows one method of disconnecting the pipe. As there shown,the pipe is made in two flanged sections 72a and72b. By removing thebolts (not shown) from the mating flanges 72c and 72d it is possible todisconnect the pipe and permit ready disassembly of the inner and outersleeve assemblies. Pipe section 72a remains connected to the innersleeve as sembly, while pipe section 72b remains attached to the outersleeve assembly. Only one pipe joint needs to be disconnected.

Fluid passage 74 is defined by the two sleeves 14 and 16 and two radialpartitions 78 and 80; the passage thus occupies onehalf of the sleevecircumference. Partitions 78 and 80 have their rear edges 82 apacedforwardly from the wet back section defined by closure plate 28and 30.Passage 74 fluid can thus flow through the wet back section and intoanother Iongitudinal passage 84 which occupies the other one-half of theexits from the heater through a tubular outlet 86 located near the frontof the heater. In actual practice outlet 86 would be offset to one sideof partition 80, hence not visible in FIG. 1.

HEAT TRANSFER ACTION It is believed that heat absorption by the fluidwhile in the heater is improved when the fluid is caused to have asignificant and positive velocity across the heater surfaces. For thisreason the water pump (not shown) is preferably operated whenever theburner is energized. If necessary the pump can be continuously energizedor it can be programmed by the same thermostat or other control whichcycles the burner.

The pump gives the water a positive velocity such that it is preventedfrom stagnating at any point in the heater. New fluid films continuallyreplace the fluid at the liquid-metal interface, thus causing the metalsurfaces on the water side to be relatively cool. For example, assuminga combustion gas temperature of 2,000 F., calculations indicate that bycausing a forced circulation of the water through the heater it ispossible to keep the metal temperatures at the liquid interfacesomewhere near 250 F., whereas the corresponding interface in aconventional tube-shell boiler would be somewhere near 370 F. The lowermetal temperatures at the metal-liquid interface provide an increasedtemperature differential between the hot gases and the heat-absorbingfluids, thus providing a greater thermal driving force and higher heatrelease rate, due to a better heat drawout action.

The illustrated heater is somewhat similar to the hater shown in U.S.Pat. 2,040,959 issued to A. F. Schumann. However in the Schumann designthe fluid passages defined by the concentric sleeves are not subdividedby means of longitudinal partitions. Therefore the fluid can flowcircumferentially as well as longitudinally; it does not have adirectional characteristic that is as pronounced or definite as in thepresent design. The present use of longitudinal partitions, coupled withpositive circulation, is believed to produce a directional fluid flowwith complete scavenging and scrubbing action at the liquid-metalinterface.

In theillustrated device the various sleeves are preferably spacedfairly close together, as for example 1% inches for the two smallsleeves, and three-fourth inch for the two larger sleeves. Thenarrowness of the passages produces relatively high fluid velocities,thereby improving the heat transfer action. Further increase in fluidvelocity can be achieved by increasing the number of radial partitions.For example, FIG. 2 shown two partitions 62 and 64 dividing the annularchamber between sleeves and 12 into two longitudinal passages. By

using four partitions in this annular space it is possible to dou-' blethe number of passages and to double the linear velocity of the fluid(because the various passages are in series flow relation).

THERMAL STRESS One major consideration in the design of a high heatrelease heater is the problem of thermal stress due to excessive heatingof the metal surfaces. The illustrated design has a fairly low thermalstress characteristic because the fluid is caused to continuously washthe metal surfaces, as previously described. Additionally the thermalstress is minimized because the inner assembly, comprising plate 32 andinner sleeves 10 and I2, is floatably disposed within the spacecircumscribed by sleeve 14. Thus, axial expansion of the inner sleeveassembly can be relieved byslight movement of the plate 32 rightwardly.

Sleeve 10 will have a higher temperature than sleeve 12, and sleeve 10may undergo some thermal elongation relative to sleeve 12. To alleviateany stress between sleeve 10, plate 32 and sleeve -12, the inner sleevemay be provided with inturned frustoconical sections 99 and 100 adjacenteither or both of its ends, said frustoconical sections being capable ofdeflecting movement incident to thermal elongation of the inner sleeve,thereby relieving the thermal stress.

FLUID CONNECTIONS Frustoconical section 99 serves as a splash deflectoror fluid distributor since it is located in partial alignment with fluidinlet 58. Thus, the incoming fluid is deflected by the conical surfaceat 99 to better fan out into passage 60. The inlet 58 would in mostcases have a diameter which is greater than the spacing between sleevesl0 and 12. Therefore the inturned wall section 99 advantageouslyprovides an enlarged space at the inlet end of passage 60, therebypermitting a single adequately sized inlet 58 to be used for admittingall of the fluid to the heater. Similarly, all the fluid can beexhausted from passage 68 through a single adequately sized crossoverpipe 72 because the enlarged fluid space provided by conical section 99permits the pipe to be adequately sized.

INSPECTION AND MAINTENANCE As previously noted, the inner sleeveassembly can be withdrawn from the space circumscribed by sleeve 14. Thepurpose in such an operation is to permit inspection of the sleevesurfaces and cleaning of any surfaces having carbon incrustationsthereon. It will be seen that when the two sections passages enables thecleaning fluid to have a relatively high velocity and to thus have athorough scrubbing action on the surfaces for removal of scale, calciumdeposits, etc.

WET BACK OPERATION It is believed that best operation, as regards heatrelease and thermal stress, is obtained when a major part of thegas-contacted surface is directly washed by the fluid being heated. Withthe present design the only inactive surfaces are baffle 32a, parts offront plate 18, and the various radial partitions. Other than theseinactive surfaces, all surfaces between the refractory 43 and stack 56are active as heat transfer surfaces.

FIG. 3 illustrates a hollow partition structure which can be employed inlieu of that flat partition construction shown in FIG. 3. Thus, as shownin FIG. 3 partition 44a for sleeve 12 can be formed as a hollowprotruding rib. The fluid in sleeve 12 can then fill the rib hollowspaces 63, and the fluid in passages 45 and 54 can transfer he'atdirectly through the rib 44a surface. Such action cools the rib andtends to prolong its service life.

In a similar manner, the baffle 32a may be more effectively cooled bymaking it in the form of a hollow fluid filled element 32b as shown inFIG. 4. In the FIG. 4 construction the baffle takes the form of a tubewelded to sleeve 14 at 33 and having small holes at spaced pointsthereon opening to water passage 74. These small holes permit automaticfill-up of the tube and venting of an excess vapor pressure. Tube 32bextends around the circumference of cylinder 14 for about 210 i.e. thesame distance as baffle 32a. The ends of the tube are of course plugged.In operation, the fluid in tube 3b tends to absorb the heat of the hotgas as it impinges on the front and rear faces of the tube, thus tendingto improve heat transfer and the service life of the baffle.

In the FIG. 4 design, maintenance operations include drawout of theinner sleeve assembly from the outer assembly, as with the design ofFIG. 1. However the tube-type baffle 32b remains with outer sleeveassembly during such drawout operations; in the FIG. 1 design the baffle32a was attached to the inner sleeve assembly and moved with it duringthe drawout operation.

The drawings shown the heater with its axis arranged horizontally.However it will be appreciated that the heater can be used in avertically oriented position. Thus, the terms front, rear, back, etc.are used in a relative sense.

FIGS. 8 AND 10 FIG. 8 illustrates a variation of the invention whereinthe rear end of the heater is closed by two flat cylindrical closureplates 28a and 30a, said plates defining a wetback section for conveyingwater or other fluid from passage 74 to passage 84. A cylindrical sleeve83 may be welded to plates 28a and 30a to form an access opening forpersonal entry into the combustion space. Refractory plug 85, equippedwith a Pyrex observation window 87, is suitably mounted in sleeve 83during normal operating periods.

The baffling of combustion gases into the various longitudinal passagesmay be accomplished by means of an arcuate plate 89, a flatsector-shaped plate 91, and two longitudinal partitions 93 and 95. Theseplates form a water space 97 which extends approximately 210 radialdegrees around the shell circumference; the remaining 150 forms a gaspassage 99 for directing hot gases from gas reversal zone 38 into thelongitudinal passage 45. The arrangement functions in a similar fashionto the water-cooled baffle 32b shown in FIG. 4 or the noncooled baffle320 shown in FIG. 1.

FIG. 9

FIG. 9 illustrates various ways of forming the longitudinal partitionswhich separate the four concentric sleeves into longitudinal passages.Thus, the partitions can be formed as inwardly directly hollow ribs, asshown at 42b, 44b, and 78a. Altemately the ribs can be mating ribsprojecting toward one another from adjacent sleeves, as shown at 62a,62b. The aim in each case is to provide a water-cooled rib structure formore extensive heat transfer and prolonged service life.

FIG. 11

FIG. 11 is similar to FIG. 8 except that the rear closure is formed by acast refractory disk 100, and the gas-directing baffle is formed by aC-cross sectioned refractory baffle element 102. The baffle is open forabout around the sleeve 12 circumference, thus providing a port foradmitting the hot combustion gases to passage 45. The gas and water flowpaths are similar to the paths previously described.

In the FIG. 11 construction the two sleeves 14 and 16 are preferablysealed at their rear edges by an annular metal plate 301:. Therefractory disk 100 may be removably clamped to plate 30b by variousmeans such as C-clamps, through bolts, hinge-latch arrangements of onetype or another, etc. The removability of the refractory permits easierreplacement should the hot gases tend to erode through the refractory.

FIGS. 12 THROUGH 14 FIGS. 12 and 13 illustrate the invention as appliedto a water heater adapted to produce steam. In this arrangement theouter tube 16 is eccentric with respect to sleeve 14 to define a steamcollection space 104. Hot gases are produced in tube 10, as in theprevious embodiments.

The hot gases produced in tube 10 impinge against cast refractoryclosure 100, as in FIG. 11. The gases are then directed into passage 45via a C-cross sectioned refractory similar to refractory 102. Innersleeve assembly 10, 12 differs slightly from that of FIG. 11 in that thetwo sleeves are cut away for about 150 radial degrees at their rearedges, as shown best in schematic FIG. 4. The C-cross sectionedrefractory 102 encircles the noncutaway areas of the tubes to thus formthe port for admitting the hot gases to the passage 45. Suitable plates,not numbered, are provided to seal the spaces formed by the cutouts inthe sleeves 10 and 12. General gas flow is similar to that previouslydescribed for FIG. 1, etc.

Water flow is somewhat different in FIGS. 12 and 13 as compared to thepreviously described embodiments. As illustratively shown in FIG. 13,the primary heat-absorbing chamber (sleeves l0 and 12) may be subdividedinto four longitudinal passages 107, 109, 111 and 113 by means of fourpartitions 108, 110, 112 and 114. Water flows rearwardly in passage107,forwardly in passage 109, rearwardly in passage 111, and forwardlyin passage 113. The various partitions are staggered toward or away fromthe front closure plate 18 to provide the fluid connections from onepassage to another. Water exits from passage 113 via crossover pipe 116which may be formed in somewhat the same fashion as pipe 72 (FIGS. 1 and7). Pipe 116 directs the water into the outer chamber 118 formed betweensleeves 14 and 16.

The water in chamber 118 is heated by the hot gases flowing throughpassages 45, 50 and 54, and by the relatively hot water received frompipe 116.

To facilitate clean out of the flue passages 45, 50 and 54, there may beformed through plate 18 a series of arcuate segmental openings or slots120 closed by one or more removable access plates 122. Conventionalbrushes may be run through these slots to dislodge soot without removingthe inner sleeve assembly. Removal of the inner assembly would then onlybe necessary forv inspection and/or repair. Similar slot-platearrangements can of course be provided in the other forms of theinvention.

I claim:

1. A fluid heater comprising four telescoping sleeves, including a firstinner sleeve, a second intermediate sleeve larger in diameter than thefirst, a third intermediate sleeve larger in diameter than the second,and a fourth outer sleeve larger in diameter than the third; frontclosure means for the annular space between the inner and outer sleeves;rear closure means for the space circumscribed by the fourth sleeve; theinner sleeve constituting a combustion tube for reception of burninggases flowing from front-to-rear; the space immediately forward of therear closure means constituting a hot gas reversal zone; the annularspace between the first and second sleeves constituting a primaryheat-absorbing chamber; the annular space between the second and thirdsleeves constituting a secondary hot gas chamber; the annular spacebetween the third and fourth sleeves constituting a secondaryheat-absorbing chamber; portmeans connecting the gas reversal zone withthe secondary hot gas chamber; said primary heat-absorbing chamber andsaid secondary hot gas chamber having longitudinal partitions thereinsubdividing the respective chambers into longitudinal passages havingsegmental cross sections, successive ones of said passages in therespective chambers having fluid connections with one another atdifferent ends of the heater whereby the hot gases and heated fluid arerequired to flow longitudinally back and forth in sinuous paths in orderto traverse the heater.

2. The heater of claim 1 comprising a baffle going across the annularspace between the second and third sleeves adjacent their rear ends;said baffle having an opening therethrough placing the hot gas reversalzone in fluid communication with one of the passages in the secondaryhot gas chamber; said opening constituting the aforementioned port meanssaid baffle comprising a hollow chamber having fluid communication withthe space between the third and fourth sleeves, whereby the baffle isfluid-cooled.

3. The fluid heater of claim 1 wherein said port means if formed by abaffle which takes takes the form of a refractory wall partiallyencircling the second sleeve.

4. The heater of claim 1 wherein the front closure means comprises afirst seal means for the annular space between the first and thirdsleeves, and a second seal means for the annular space between the thirdand fourth sleeves; the first and second sleeves cooperating with thefirst seal means to form an integral subassembly which can be drawn outof the space circumscribed by the third sleeve.

5. The heater of claim 4 and further comprising a fluid crossover pipeconnecting one of the passages in the primary heatabsorbing chamber withone of the passages in the secondary heat-absorbing chamber; said'pipehaving one of its ends attached to the first seal means and its otherend attached to the fourth sleeve; said pipe being located outside thefour sleeves whereby disconnection of the pipe allows the aforementionedsubassembly to be drawn out from the space circumscribed by the thirdsleeve.

6. The heater of claim 1 and further comprising fluid inlet meansmounted on the front closure means in direct connection with one of thepassages in the primary heat-absorbing chamber.

7. The heater of claim 1 wherein the first sleeve is provided with anintumed wall section adjacent at least one of its ends; said intumedwall section being capable of deflecting movements incident to thermalelongation of the first sleeve, thereby relieving thermal stress.

8. The heater of claim 1 wherein at least some of the longitudinalpartitions are formed as hollow ribs protruding from the sleeves; saidhollow ribs being integral with the sleeves so that sleeve fluid or gasflows into the rib hollow spaces.

9. The heater of claim 1 wherein the longitudinal partitions in thesecondary hot gas chamber are shorter than the chamber length;successive ones of said last-mentioned partitions being alternatelystaggered toward or away from the front closure means, whereby thespaces between the end edges of the partitions and adjacent closuremeans constitute gas flow openings.

10. The heater of claim 1 wherein the partitions between the second andthird sleeves comprise three partitions cooperating to define threepassages arranged in series flow relation, the first one of the threepassages being about 150 radial degrees measured circumferentially, thesecond one of the three passages being about 120 radial degrees measuredcircumferentially, and the third one of the three passages being aboutmeasured circumferentially.

11. A fluid heater comprising a plurality of telescoping sleevesarranged one within another to define a central hot gas chamber, and aseries of annular chambers surrounding said central chamber; at leastone of said annular chambers being connected with the central chamber toreceive hot gases therefrom; at least one of the annular chambers beingadapted to have heat-absorbing fluid flow therethrough; at least some ofthe annular hot gas chambers and some of the annular fluid chambershaving longitudinal partitions therein subdividing same intolongitudinal passages, which are in succession connected together atdifferent ends of the heater whereby the hot gases and heated fluid arecaused to flow longitudinally back and forth in sinuous paths as theytraverse their respective chambers.

1. A fluid heater comprising four telescoping sleeves, including a firstinner sleeve, a second intermediate sleeve larger in diameter than thefirst, a third intermediate sleeve larger in diameter than the second,and a fourth outer sleeve larger in diameter than the third; frontclosure means for the annular space between the inner and outer sleeves;rear closure means for the space circumscribed by the fourth sleeve; theinner sleeve constituting a combustion tube for reception of burninggases flowing from front-to-rear; the space immediately forward of therear closure means constituting a hot gas reversal zone; the annularspace between the first and second sleeves constituting a primaryheat-absorbing chamber; the annular space between the second and thirdsleeves constituting a secondary hot gas chamber; the annular spacebetween the third and fourth sleeves constituting a secondaryheat-absorbing chamber; port means connecting the gas reversal zone withthe secondary hot gas chamber; said primary heat-absorbing chamber andsaid secondary hot gas chamber having longitudinal partitions thereinsubdividing the respective chambers into longitudinal passages havingsegmental cross sections, successive ones of said passages in therespective chambers having fluid connections with one another atdifferent ends of the heater whereby the hot gases and heated fluid arerequired to flow longitudinally back and forth in sinuous paths in orderto traverse the heater.
 2. The heater of claim 1 comprising a bafflegoing across the annular space between the second and third sleevesadjacent their rear ends; said baffle having an opening therethroughplacing the hot gas reversal zone in fluid communication with one of thepassages in the secondary hot gas chamber; said opening constituting theaforementioned port means said baffle comprising a hollow chamber havingfluid communication with the space between the third and fourth sleeves,whereby the baffle is fluid-cooled.
 3. The fluid heater of claim 1wherein said port means if formed by a baffle which takes takes the formof a refractory wall partially encircling the second sleeve.
 4. Theheater of claim 1 wherein the front closure means comprises a first sealmeans for the annular space between the first and third sleeves, and asecond seal means for the annular space between the third and fourthsleeves; the first and second sleeves cooperating with the first sealmeans to form an integral subassembly which can be drawn out of thespace circumscribed by the third sleeve.
 5. The heater of claim 4 andfurther comprising a fluid crossover pipe connecting one of the passagesin the primary heat-absorbing chamber with one of the passages in thesecondary heat-absorbing chamber; said pipe having one of its endsattached to the first seal means and its other end attached to thefourth sleeve; said pipe being located outside the four sleeves wherebydisconnection of the pipe allows the aforementioned subassembly to bedrawn out from the space circumscribed by the third sleeve.
 6. Theheater of claim 1 and further comprising fluid inlet means mounted onthe front closure means in direct connection with one of the passages inthe primary heat-absorbing chamber.
 7. The heater of claim 1 wherein thefirst sleeve is provided with an inturned wall section adjacent at leastone of its ends; said inturned wall section being capable of deflectingmovements incident to thermal elongation of the first sleeve, therebyrelieving thermal stress.
 8. The heater of claim 1 wherein at least someof the longitudinal partitions are formed as hollow ribs protruding fromthe sleeves; said hollow ribs being integral with the sleeves so thatsleeve fluid or gas flows into the rib hollow spaces.
 9. The heater ofclaim 1 wherein the longitudinal partitions in the secondary hot gaschamber are shorter than the chamber length; successive ones of saidlast-mentioned partitions being alternately staggered toward or awayfrom the front closure means, whereby the spaces between the end edgesof the partitions and adjacent closure means constitute gas flowopenings.
 10. The heater of claim 1 wherein the partitions between thesecond and third sleeves comprise three partitions cooperating to definethree passages arranged in series flow relation, the first one of thethree passages being about 150 radial degrees measuredcircumferentially, the second one of the three passages being about 120radial degrees measured circumferentially, and the third one of thethree passages being about 90* measured circumferentially.
 11. A fluidheater comprising a plurality of telescoping sleeves arranged one withinanother to define a central hot gas chamber, and a series of annularchambers surrounding said central chamber; at least one of said annularchambers being connected with the central chamber to receive hot gasestherefrom; at least one of the annular chambers being adapted to haveheat-absorbing fluid flow therethrough; at least some of the annular hotgas chambers and some of the annular fluid chambers having longitudinalpartitions therein subdividing same into longitudinal passages, whichare in succession connected together at different ends of the heaterwhereby the hot gases and heated fluid are caused to flow longitudinallyback and forth in sinuous paths as they traverse their respectivechambers.